Method and apparatus for managing contention window in wireless communication system

ABSTRACT

A base station is provided. The base station transmits multiple data in a first subframe, receives response signals corresponding to the multiple data, determines a ratio of negative acknowledge (NACK) signals to the response signals, and adjusts or maintains a contention window based on the determined ratio. The present disclosure relates to communication schemes for combining 5th-generation (5G) communication systems with internet of things (IoT) technology to support higher data transmission rate as post-4th-generation (post-4G) systems and systems for the same. The present disclosure may be used in intelligent services (e.g., smart home, smart building, smart city, smart car, or connected car, health-care, digital education, retail business, security and safety-related services, etc.) based on the 5G communication technology and IoT-related techniques.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 15/154,558, filed on May 13, 2016, which has issued as U.S. Pat. No.10,142,079 on Nov. 27, 2018 and was based on and claimed priority under35 U.S.C. § 119(e) of a U.S. Provisional application No. 62/161,398,filed on May 14, 2015 in the U.S. Patent and Trademark Office, thedisclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to methods and apparatuses for managing acontention window in wireless communication systems.

BACKGROUND

In order to meet the demand for wireless data traffic soaring since the4th generation (4G) communication system came to the market, there areongoing efforts to develop enhanced 5th generation (5G) communicationsystems or pre-5G communication systems. For the reasons, the 5Gcommunication system or pre-5G communication system is called the beyond4G network communication system or post long term evolution (LTE)system.

For higher data transmit rates, 5G communication systems are consideredto be implemented on ultra-high frequency bands (mmWave), such as, e.g.,60 GHz. To mitigate pathloss on the ultra-high frequency band andincrease the reach of radio waves, the following techniques are takeninto account for the 5G communication system: beamforming, massivemulti-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), arrayantenna, analog beamforming, and large scale antenna.

Also being developed are various technologies for the 5G communicationsystem to have an enhanced network, such as evolved or advanced smallcell, cloud radio access network (cloud RAN), ultra-dense network,device-to-device (D2D) communication, wireless backhaul, moving network,cooperative communication, coordinated multi-point (CoMP), andinterference cancellation.

There are also other various schemes under development for the 5G systemincluding, e.g., hybrid frequency shift keying (FSK) and quadratureamplitude modulation (QAM) modulation (FQAM) and sliding windowsuperposition coding (SWSC), which are advanced coding modulation (ACM)schemes, and filter bank multi-carrier (FBMC), non-orthogonal multipleaccess (NOMA) and sparse code multiple access (SCMA), which are advancedaccess schemes.

The internet is evolving from the human-centered connection network bywhich humans create and consume information to the internet of things(IoT) network by which information is communicated and processed betweenthings or other distributed components. The internet of everything (IoE)technology may be an example of a combination of the big data processingtechnology and the IoT technology through, e.g., a connection with acloud server.

To implement the IoT, technology elements, such as a sensing technology,wired/wireless communication and network infra, service interfacetechnology, and a security technology, are required. There is a recentongoing research for inter-object connection technologies, such as thesensor network, machine-to-machine (M2M), or the machine-typecommunication (MTC).

In the IoT environment may be offered intelligent internet technology(IT) services that collect and analyze the data generated by the thingsconnected with one another to create human life a new value. The IoT mayhave various applications, such as the smart home, smart building, smartcity, smart car or connected car, smart grid, health-care, or smartappliance industry, or state-of-art medical services, through conversionor integration of existing IT technologies and various industries.

Thus, there are various ongoing efforts to apply the 5G communicationsystem to the IoT network. For example, the sensor network, M2M, MTC, orother 5G techniques are implemented by schemes, such as beamforming,MIMO, and array antenna schemes. The above-mentioned application of thecloud radio access network as a big data processing technique may besaid to be an example of the convergence of the 5G and IoT technologies.

Recent mobile communication systems are evolving to high-speed,high-quality wireless packet data communication systems to provide dataservices and multimedia services beyond the initial versions that haveprovided voice-centered services. Recently there have been developed tosupport high-speed, high-quality wireless packet data transmissionservices, various mobile communication standards, such as 3rd generationpartnership project (3GPP) high speed downlink packet access (HSDPA),high speed uplink packet access (HSUPA), LTE, LTE-advanced (LTE-A),3GPP2 high rate packet data (HRPD), and institute of electrical andelectronics engineers (IEEE) 802.16. In particular, the LTE/LTE-A system(hereinafter, LTE system) happened to have the maximum frequencyefficiency while undergoing continuous development of standards andevolution.

Further, data transmission rate and system capability have beenmaximized using carrier aggregation (CA) by which the system may beoperated via multiple frequency bands. However, the frequency bandoperated by the current LTE system is the licensed band (the licensedspectrum or licensed carrier) which the service provider generally has adedicated right to use. Generally, since the frequency band (e.g., a 5GHz or less frequency band) on which mobile communication services arenow being offered is already occupied and used by other serviceproviders or other communication systems, the service provider hasdifficulty securing and operating multiple licensed bands to expand thesystem capability.

There are being recently researched techniques to utilize, for the LTEsystem, the unlicensed band (unlicensed spectrum or unlicensed carrier)relatively easy to secure in order to process mobile data thatexplosively increases and to address the issue of securing frequency.Among frequency bands in unlicensed bands, particularly the 5 GHz bandis used by a relatively small number of devices and allows forutilization of a significantly wide bandwidth. Accordingly, the use ofthe 5 GHz unlicensed band facilitates to maximize the LTE systemcapacity.

For example, multiple frequency bands may be utilized based on the CAtechnique which is one major technology for the LTE system. That is, theLTE cell on the licensed band and the LTE cell (licensed assisted access(LAA) cell or LTE-unlicensed spectrum (LTE-U) cell) on the unlicensedband may be considered the primary cell (PCell (or Pcell)) and thesecondary cell (SCell (or Scell)), respectively, to operate the LTEsystem on the unlicensed band in a manner equal or similar to the legacyCA environment. In this case, the LTE system may be applicable to thedual-connectivity environment where the licensed band and the unlicensedband are connected with each other via a non-ideal backhaul as well asthe CA where the licensed band and the unlicensed band are connectedwith each other via an ideal backhaul.

The orthogonal frequency division multiplexing (OFDM) scheme typicallyused in the LTE system transmits data via multiple carriers, and this isa sort of multi-carrier modulation scheme that parallelizes symbolsequences inputted in series and modulates the same into multiplemulti-carriers, i.e., multiple subcarrier channels with mutualorthogonality and transmits the same.

In the OFDM scheme, a modulated signal is positioned in a 2-dimensionalresource constituted of time and frequency. The resources on the timeaxis are differentiated by different OFDM symbols and they areorthogonal to each other. The resources on the frequency axis aredifferentiated by different subcarriers and they are also orthogonal toeach other. In the OFDM scheme, one minimum unit resource may beindicated by designating a particular OFDM symbol on the time axis and aparticular subcarrier on the frequency axis, and this is called aresource element (RE). Since different REs maintain the orthogonalityeven when undergoing frequency selective channel, signals transmittedvia different REs may be received on the reception side without mutualinterference.

The physical channel is a channel of a physical layer transmitting amodulated symbol obtained by modulating one or more coded bit streams.The orthogonal frequency division multiple access (OFDMA) systemconfigures and transmits a plurality of physical channels depending onthe receiver or the purpose of information streams transmitted. The REwhere one physical channel should be disposed and transmitted should bepreviously agreed between the transmitter and the receiver, and suchrule is referred to as mapping.

In the OFDM communication system, a downlink bandwidth includes multipleresource blocks (RBs), and each physical RB (PRB) may include 12subcarriers arranged along the frequency axis and 14 or 12 OFDM symbolsarranged along the time axis. Here, the PRB is a basic unit for resourceallocation.

The reference signal (RS) is a signal transmitted by the base stationfor a user equipment (UE) to perform channel estimation. The RSs for theLTE communication system include the common RS (CRS) and thedemodulation RS (DMRS) which is a dedicated RS.

The CRS is an RS transmitted over the overall downlink band andreceivable by all the UEs and is used for channel estimation,configuring feedback information by the UE, and demodulation of datachannel. The DMRS is an RS transmitted over the overall downlink band.The DMRS is used for demodulation of a data channel by a particular UEand channel estimation, but not used for configuring feedbackinformation unlike the CRS. Accordingly, the DMRS is transmitted througha PRB resource that is to be scheduled by the UE.

A subframe on the time axis consists of two 0.5 msec-long slots, i.e., afirst slot and a second slot. The physical dedicated control channel(PDCCH) region that is a control channel region and the ePDCCH (enhancedPDCCH) region that is a data channel region are separately transmittedon the time axis. This is for quickly receiving and demodulating controlchannel signals. Further, the PDCCH region is positioned on the overalldownlink band and this has the form that one control channel is splitinto smaller units of control channels that are distributed andpositioned over the entire downlink band.

The uplink generally comes largely in the physical uplink controlchannel (PUCCH), which is a control channel and a physical uplink sharedchannel (PUSCH), which is a data channel. A response signal and otherfeedback information for the downlink data channel, unless there is adata channel, are transmitted through a control channel, and if any datachannel, through the data channel.

Meanwhile, a base station in an LTE cell may communicate with a UE usingan unlicensed band in addition to the existing licensed band that it isusing. In such case, the LTE cell where the licensed band is availablemay be denoted as a PCell, and the LAA cell where the unlicensed band isavailable may be denoted as an SCell.

When the base station uses the unlicensed band, it needs to perform,e.g., a channel occupancy operation appropriate for the unlicensed band.However, the legacy operation of unlicensed band has somethinginappropriate for the communication characteristics of the LTE cell basestation and suffers from the issue that the operation of the basestation is not smoothly done on the unlicensed band. For example,although the contention window on the unlicensed band is configuredbased on a response signal received from one UE, the base station mayreceive response signals from multiple UEs at the same time whichrenders ambiguous standards for configuring the contention window. Thus,there is required a method for the base station to smoothly performcommunication on the unlicensed band.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentdisclosure is to provide a method and apparatus for managing acontention window in a wireless communication system.

According to an embodiment of the present disclosure, there are proposeda method and apparatus for accessing a channel of an unlicensed band ina wireless communication system.

Another aspect of the present disclosure is to provide a channeloccupancy method and apparatus by a base station on an unlicensed band.

Another aspect of the present disclosure is to provide a method andapparatus for allowing an unlicensed band to be used as an additionalchannel for communication.

In accordance with an aspect of the present disclosure, a method formanaging a contention window by a base station in a wirelesscommunication system is provided. The method includes transmittingmultiple data in a first subframe, receiving response signalscorresponding to the multiple data, determining a ratio of negativeacknowledge (NACK) signals to the response signals, and adjusting ormaintaining the contention window based on the determined ratio.

In accordance with another aspect of the present disclosure, a basestation in a wireless communication system is provided. The base stationincludes a transmitter configured to transmit multiple data in a firstsubframe, a receiver configured to receive response signalscorresponding to the multiple data, and a controller configured todetermine a ratio of NACK signals to the response signals and adjustingor maintaining the contention window based on the determined ratio.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1A is a view illustrating an example of a wireless communicationsystem according to an embodiment of the present disclosure;

FIG. 1B is a view illustrating another example of a wirelesscommunication system according to an embodiment of the presentdisclosure;

FIG. 2 is a view illustrating a structure of a subframe for a channelsensing and occupying operation on an unlicensed band according to anembodiment of the present disclosure;

FIG. 3 is a view illustrating a channel access scheme for an unlicensedband of a Wi-Fi system according to an embodiment of the presentdisclosure;

FIG. 4 is a flowchart illustrating a process in which a licensedassisted access (LAA) cell occupies a channel of an unlicensed band toperform data transmission according to an embodiment of the presentdisclosure;

FIG. 5 is a view illustrating the temporal relation between LAA cell anduser equipments (UEs) according to data communication according to anembodiment of the present disclosure;

FIG. 6 is a view illustrating an example in which a contention window isconfigured per transmission of data and control information according toan embodiment of the present disclosure;

FIG. 7 is a flowchart illustrating a method for configuring a contentionwindow for a channel sensing operation according to an embodiment of thepresent disclosure;

FIG. 8 is a block diagram illustrating a base station according to anembodiment of the present disclosure; and

FIG. 9 is a block diagram illustrating a UE according to an embodimentof the present disclosure.

Throughout the drawings it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

Prior to going into the detailed description of the present disclosure,it might be effective to define particular words and phrases as usedherein. As used herein, the terms “include” and “comprise” and theirderivatives may mean doing so without any limitations. As used herein,the term “or” may mean “and/or.” As used herein, the phrase “associatedwith” and “associated therewith” and their derivatives may mean“include,” “be included within,” “interconnect with,” “contain,” “becontained within,” “connect to or with,” “couple to or with,” “becommunicable with,” “cooperate with,” “interleave,” “juxtapose,” “beproximate to,” “be bound to or with,” “have,” or “have a property of.”As used herein, the term “controller” may mean any device, system, orpart thereof controlling at least one operation. As used herein, theterm “device” may be implemented in hardware, firmware, software, orsome combinations of at least two thereof. It should be noted thatfunctions, whatever particular controller is associated therewith, maybe concentrated or distributed or implemented locally or remotely. Itshould be appreciated by one of ordinary skill in the art that thedefinitions of particular terms or phrases as used herein may be adoptedfor existing or future in many cases or even though not in most cases.

Hereinafter, according to the present disclosure, the long termevolution (LTE) system and the LTE-advanced (LTE-A) system are describedas examples, but the present disclosure may also apply to othercommunication systems using a licensed band and unlicensed band withoutlimited thereto.

FIG. 1A is a view illustrating an example of a wireless communicationsystem according to an embodiment of the present disclosure.

Referring to FIG. 1A, the wireless communication system includes a basestation 101 and a user equipment (UE) 104. The base station 101 may be,e.g., a small base station. The cell of the base station 101 may includean LTE cell 102 and a licensed assisted access (LAA) cell 103. The LTEcell 102 denotes a cell where the UE 104 uses a licensed band 105 toperform data communication with the base station 101. The LAA cell 103denotes a cell where the UE 104 uses an unlicensed band 106 to performdata communication with the base station 101. There is no limitation onthe duplex scheme of the LTE cell 102 or LAA cell 103. However, uplinktransmission may be limited as performed only through the LTE cell 102when the LTE cell 102 is a primary cell (PCell).

FIG. 1B is a view illustrating another example of a wirelesscommunication system according to an embodiment of the presentdisclosure.

Referring to FIG. 1B, the wireless communication system may include anLTE macro base station 111 for broad coverage in the network and an LAAsmall base station 112 for increasing the amount of data transmitted.The UE 114 may perform data communication with the LTE macro basestation 111 using the licensed band 116 and data communication with theLTE macro base station 111 using the unlicensed band 115. There is nolimitation on the duplex scheme of the LTE macro base station 111 or LAAsmall base station 112. However, uplink transmission may be configuredto be performed only through the LTE macro base station 111 when the LTEmacro base station 111 is a PCell. Here, the LTE macro base station 111and the LAA small base station 112 may have an ideal backhaul networkthat is based on a base station interface, such as an X2 interface 113.Thus, quick inter-base station communication is possible, and even whenuplink transmissions are sent only to the LTE macro base station 111,the LAA small base station 112 may receive, in real-time, relevantcontrol information from the LTE macro base station 111 throughinter-base station communication.

Generally, for the unlicensed band, the same frequency band is sharedand used by a plurality of devices. At this time, the devices using theunlicensed band may be of the same or different systems. Accordingly,typical operations of the devices operated on the unlicensed band formutual co-existence among various devices are as follows. A transmissiondevice requiring signal transmission including data or control signalsidentifies the channel occupancy state by other devices for the radiochannel which are to perform signal transmission and radio channelpreviously selected, and depending on the determined channel occupancystate, may or might not occupy the channel. Such operation is generallycalled listen-before-talk (LBT).

In other words, the transmitter should sense the channel during apredetermined time and determine whether the channel is occupied. Atthis time, the time to sense the channel may be previously defined orarbitrarily selected. Further, the channel sensing time may be set inproportion to a maximum channel occupancy time as set. The channelsensing operation to determine whether to occupy the channel may be setdifferently depending on unlicensed frequency bands, regions, orper-country regulations. For example, in the U.S., the unlicensed bandmay be used without a separate channel sensing operation other than theoperation for radar sensing on the 5 GHz frequency band.

The transmitter intending to use an unlicensed band, when not sensingother devices using the channel through the channel sensing operation(or LBT), can use the channel. Here, upon operation, the devices usingthe unlicensed band may set the maximum channel occupancy time duringwhich they may occupy the channel. Here, the maximum channel occupancytime may be previously set as per a defined regulation or based oninformation received from other device. For example, the UE may set themaximum channel occupancy time by receiving configured information fromthe base station.

Further, the maximum channel occupancy time may be set differentlydepending on different unlicensed bands or per-local or per-countryregulations. For example, in Japan, the maximum channel occupancy timeon the unlicensed band of 5 GHz is limited to 4 ms. By contrast, inEurope, the channel may be occupied and used for up to l0 ms or 13 ms.Accordingly, devices using unlicensed band may use the channel for themaximum channel occupancy time set by the corresponding band and localor central governmental regulations. The devices having occupied thechannel during the maximum channel occupancy time, in order to reoccupythe channel, performs the channel sensing operation again and they mayoccupy or not depending on whether other devices use the band.

The channel sensing and occupying operations on the unlicensed band aredescribed in detail with reference to FIG. 2.

FIG. 2 is a view illustrating a structure of a subframe for a channelsensing and occupying operation on an unlicensed band according to anembodiment of the present disclosure.

Referring to FIG. 2, a process in which the base station transmits dataor control signals to the UE is described as an example. However,embodiments of the present disclosure are not limited to the examplewhere the base station transmits signals to the UE and may rather applyto situations where the UE transmits signals to the base station andhave various applications in signal transmission between devices usingthe unlicensed band.

Referring to FIG. 2, a lms-long subframe 200 includes a plurality oforthogonal frequency division multiplexing (OFDM) symbols. The basestation and the UE communicable on the unlicensed band using theunlicensed band may occupy the channel to perform communication during apreset channel occupancy time (or transmission opportunity (TXOP)) 250.In a case where the base station has an additional signal supposed to betransmitted when the preset channel occupancy time 250 expires, the basestation performs a channel sensing operation in a channel sensinginterval 220. The base station may reoccupy and use the channeldepending on the result of the channel sensing operation.

The channel sensing interval 220 may be previously set between the basestation and the UE or may be set and transferred by the base station tothe UE through, e.g., higher layer signaling. Here, the channel sensinginterval 220 may be set differently depending on frequency bands orlocally or per-country regulations defined. Further, the channel sensinginterval 220 may be set in proportion to the channel occupancy time 250.As an example, among the regulations on the 5 GHz band in Europe, thechannel sensing and occupying operations for load-based equipment aredescribed as an example.

When the base station needs additional use of the channel after themaximum channel occupancy time, it determines whether other devicesoccupy the channel during a minimum channel sensing interval. Here, theminimum channel sensing interval may be determined by the followingEquation 1 depending on the maximum channel occupancy interval.

maximum channel occupancy interval,13/32×q,(q=4, . . . ,32)

minimum channel sensing interval,ECCA slot×rand(1,q)  Equation 1

In Equation 1 above, extended clear channel assessment (ECCA) slotdenotes the minimum unit of the arbitrarily set channel sensinginterval, and rand(1, q) denotes a value arbitrarily selected fromvalues 1 to q. Accordingly, the minimum channel sensing interval may bethe multiple of ECCA slot and the arbitrarily selected value. Meanwhile,the maximum channel occupancy interval may be determined based on q. Forexample, when q is set to 32 (q=32), the maximum channel occupancyinterval may be 13 ms. Accordingly, the corresponding device may occupythe channel for up to 13 ms. As such, since the maximum channeloccupancy interval and the minimum channel sensing interval may increaseor decrease depending on q, the minimum channel sensing interval may beset to increase as the maximum channel occupancy interval increases.

Meanwhile, as set forth in Equation 1, the method for setting themaximum channel occupancy interval and the minimum channel sensinginterval is a mere example, may be applied differently depending onfrequency bands or locally or per-country regulations defined, and maybe changed in the future as the frequency regulations are modified.Further, additional operations (e.g., introduction of additional channelsensing intervals) other than the channel sensing operation according tothe frequency regulation may be included.

Not sensing other devices to use the unlicensed band during the channelsensing interval 220, that is, when the unlicensed band channel isdetermined to be in an idle state, the base station may immediatelyoccupy and use the channel. Here, the determination as to whether otherdevices occupy the channel during the channel sensing interval 220 maybe defined in advance or may be made using a preset threshold value.

For example, when the magnitude of signals received from the otherdevices during the channel sensing interval is larger than apredetermined threshold value (e.g., −62 dBm), the channel may bedetermined to have been occupied by the other devices. If the magnitudeof the signal received is equal or smaller than the threshold value, thebase station may determine that the channel is in an idle state. Thedetermination as to whether other devices occupy the channel during thechannel sensing interval 220 may be performed based on various methodsincluding, e.g., a method for detecting a pre-defined signal, inaddition to the method based on the magnitude of received signals.

The base station may sense an idle channel and start channel occupancyin a particular OFDM symbol interval in the subframe depending on theresult of channel sensing during the channel sensing interval 220.However, since the general LTE system operates in subframe units, (e.g.,performing signal transmission and reception from the first OFDM symbolof the subframe), it might not transmit or receive signals in aparticular OFDM symbol as described above. Accordingly, when sensing theidle channel during the channel sensing interval 220 of the subframe,the base station may transmit a signal for channel occupancy during aninterval 230 from when the channel sensing interval 220 expires toimmediately before the first OFDM symbol of a next subframe istransmitted.

Specifically, before transmitting a first signal (e.g., a control signaland data signal) transmitted in the subframe 210 or 240, the basestation may transmit a second signal (e.g., a first sync signal (primarysynchronization signal (PSS)/secondary synchronization signal(SSS)/common reference signal (CRS) or a newly defined signal) in orderto occupy the channel for the unlicensed band. The second signal mightnot be transmitted depending on the time when the channel sensingoperation terminates. Further, when the time when the channel starts tobe occupied is set to be within a particular OFDM symbol, the basestation may transmit a newly defined third signal until a next OFDMsymbol starts and may then transmit the second signal or first signal.For ease of description, the channel sensing interval 220 is describedusing OFDM symbol units, but the channel sensing interval 220 may be setregardless of the OFDM symbol of the LTE system.

The second signal may include a signal generated by recycling thePSS/SSS/CRS, using a sequence different from the root sequence beingused by the current licensed band, or using at least one of the PSS andthe SSS. Further, the second signal may be generated using a sequenceother than the PSS/SSS sequence necessary for generating an unlicensedband base station unique value (Cell ID) and may be used not to beconfused with the base station unique value. Further, the second signalmay include at least one of the CRS or the channel state information RS(CSI-RS), the (enhanced) physical dedicated control channel ((E)PDCCH)or physical downlink shared channel (PDSCH) or a signal which is amodification to the signal.

The interval 230 during which the second signal is transmitted isincluded in the channel occupancy time, and thus, the frequencyefficiency may be maximized when minimum information may be transferredthrough the second signal.

The LTE system using the unlicensed band as described above(hereinafter, LAA or LAA cell) is required to meet the regulations forthe unlicensed band to be used and requires a new-type channel access(or LBT) scheme different from the existing one using the licensed bandfor co-existence with other systems (hereinafter Wi-Fi) using theunlicensed band. A channel access scheme for using the unlicensed bandof the Wi-Fi system is briefly described below with reference to FIG. 3.

FIG. 3 is a view illustrating a channel access scheme for an unlicensedband of a Wi-Fi system according to an embodiment of the presentdisclosure.

Referring to FIG. 3, the AP1 310, which is a Wi-Fi access point (AP),should perform a channel sensing operation for a channel to occupy thechannel when required to transmit data to the STA1 315, which is a firstUE. Here, the channel is typically sensed during a distributedcoordination function interframe space (DIFS) interval 330. The AP1 310may occupy the channel to transmit data to the UE when determining thatthe channel is idle during the DIFS interval 330. The operation ofdetermining whether to occupy the channel during the DIFS interval 330may be performed by various methods, such as determining whether thechannel is occupied based on, e.g., the strength of signal receivedduring the time or whether a previously defined signal is detected. Whendetermined that the channel is occupied by another device, such as AP2320, during the DIFS interval 330, the AP1 310 selects any value Nwithin a preset contention window (e.g., 1 to 16). The AP1 310configures a backoff interval 355 having a length of the selected N andperforms a backoff operation.

The AP1 310 senses the channel during a predetermined time (e.g., 9 us),and upon determining that the channel is in the idle state, deducts fromN to reduce the backoff interval 355 (i.e., N=N−1). In contrast, upondetermining that other device occupies the channel during a preset time,the AP1 310 may maintain the backoff interval 355 without changing N.

When the STA2 325, which is a second UE, receives data 340 transmittedfrom the AP2 320, the STA2 325 transmits an acknowledge (ACK) ornegative ACK (NACK) 347 for the reception of data 340 to the AP2 320after a short interframe space (SIFS) time 345. Here, the STA2 325 maytransmit the ACK/NACK (A/N) 347 without performing a separate channelsensing operation. After the STA2 325 terminates the transmission of theACK or NACK 347, the AP1 310 may be aware that the channel is idle.Here, the AP1 310 senses the channel during a preset time (e.g., 9 us)after the DIFS interval 350. The AP1 310 deducts from N when determiningthat the channel is idle and sets the backoff interval 357 (That is,N=N−1).

When N=0, the AP1 310 may occupy the channel and transmit data 360 tothe STA1 315. Then, the STA1 315 may receive the data 360, and after theSIFS, the STA1 315 may transmit an ACK or NACK 370 for the reception ofthe data to the AP1 310. When the AP1 310 receives the NACK from theSTA1 315, the AP1 310 increases the contention window and selects avalue N within the increased contention window. For example, when thecontention window is [1,16], the AP1 310 receiving the NACK may changethe contention window into [1,32] and select a number, N, from 1 to 32.

In the case of the Wi-Fi system, communication is generally performedbetween one AP (or base station) and one STA (or UE) in the same time.Further, as denoted with reference numbers 347 and 370 of FIG. 3, theSTA transmits a data reception state (e.g., an ACK or NACK) to the AP(or base station) right after reception of the data. At this time, theAP1 310 or the AP2 320 performs a next data transmission operation afterreceiving the ACK or NACK from the STA1 315 or the STA2 325.

In the case of LAA system, however, the base station may transmit datato a plurality of UEs in the same time. Further, one or more UEsreceiving the data at the same time (e.g., time n) may transmit ACKs orNACKs to the base station at the same time (e.g., n+4 for the frequencydivision duplexing (FDD)). Accordingly, the LAA base station may receiveACKs or NACKs from one or more UEs at the same time unlike the Wi-Fisystem. Further, at least 4 ms or more of data transmission time gap mayoccur between the time when the UE transmits the A/N and the time whenthe base station transmits data. That is, when the LAA base stationconfigures a contention window by the transmission of A/N from the UE asin the Wi-Fi, the base station can receive A/Ns from a plurality of UEsat a particular time, and thus, ambiguity may arise in configuring thecontention window. Further, the time of applying the contention window(re)set is unclear due to a transmission delay of A/N from the UE.

Accordingly, according to an embodiment of the present disclosure, thereare proposed a method and apparatus by which an LAA base station maymore clearly configure a contention window based on A/N informationreceived from a UE.

According to an embodiment of the present disclosure, there aredescribed a method and apparatus that allow an LTE system to be properlyoperated on an unlicensed band by reflecting the operationalcharacteristics on the unlicensed band as described above.

Although only carrier aggregation (CA) environments are assumed anddescribed for ease of description according to an embodiment of thepresent disclosure, the present disclosure is not limited thereto andmay also be applicable to stand-alone environments in which it operatesonly under dual-connectivity or unlicensed band environments.

Further, according to an embodiment of the present disclosure, thedescription primarily focuses on the downlink where transmission occursfrom the base station to the UE in the general LTE system for ease ofdescription. That is, the transmission device requiring signaltransmission is represented as the base station, and the transmissiondevice requiring signal reception is represented as the UE. However, thepresent disclosure may also be applicable to the uplink wheretransmission occurs from the UE to the base station without limitationsas well as the downlink and may apply in the operation of the generaltransmission device or reception device.

Hereinafter, a process in which the base station of the LTE cell(hereinafter, a “LAA cell”) occupies an unlicensed band to perform datatransmission is described with reference to FIG. 4.

FIG. 4 is a flowchart illustrating a process in which an LAA celloccupies a channel of an unlicensed band to perform data transmissionaccording to an embodiment of the present disclosure.

Referring to FIG. 4, the LAA cell maintains the idle state where no datatransmission is required in operation 401. The idle state includes astate where the LAA cell does not transmit data on the unlicensed band.

The LAA cell determines whether channel occupancy is needed for datatransmission in operation 402. When determining that channel occupancyis needed, the LAA cell performs a first channel sensing operation inoperation 403. Here, the LAA cell may set the contention window used fora second channel sensing operation as an initial value. The firstchannel sensing operation includes an operation for determining thechannel occupancy state based on at least one of the strength of asignal received during a preset time and whether a pre-defined signal isdetected. The first channel sensing time during which the first channelsensing operation may be performed may be set as a preset value or resetby the base station.

When determining that the channel is in the idle state as a result ofthe first channel sensing operation in operation 404, the LAA cell mayoccupy the channel and transmit data in operation 405. In contrast, whendetermining that the channel is occupied by other devices in operation404, the LAA cell may select a variable N within the contention window[x, y] set in operation 407. Here, the contention window may bepreviously set or (re)set by the base station. Further, the contentionwindow may be set using, e.g., the number of times of attempting tooccupy the channel, occupancy rate for the channel (e.g., traffic load),or result of receiving data signals transmitted upon channel occupancyby the UE (e.g., A/N).

For example, when the LAA cell occupying the channel in operation 405 isdetermined to additionally need to occupy the channel in operation 406,the contention window may be reset in operation 414 based on the resultof the data transmission performed in operation 405. Here, the scheme ofresetting the contention window using the data transmission result is amere example, and the contention window may be reset by a preset valueor the operation of previously occupying the channel and transmittingdata.

For example, when transmitting data to the UE during the configurationinformation and receiving an NACK as a result of the data transmissionfrom the UE, the LAA cell may increase the contention window. When theLAA cell occupying the increased contention window transmits data to theUE during the channel occupancy interval and receives an ACK as a resultof reception for the data transmission from the UE, the LAA cell mayreduce the contention window or set the contention window as an initialvalue. The scheme of configuring the contention window using the A/N isa mere example, and the contention window may be reset using otherreferences.

When a variable N is set during the contention window in operation 407,the LAA cell may perform the second channel sensing operation inoperation 408. The second channel sensing operation may be the same asthe first channel sensing operation or may be performed during a secondchannel sensing time shorter than the first channel sensing time. Forexample, the first channel sensing time may be set to 34 us, and thesecond channel sensing time may be set to 9 us.

The second channel sensing operation may include an operation fordetermining the channel occupancy state based on at least one of thestrength of signal received during a preset time and whether apredetermined signal is detected and may be set to be different from thefirst channel sensing operation. When determining that the channelsensed in operation 408 is an idle channel in operation 409, the LAAcell deducts one from the variable N in operation 410. When the value Ndeducted in operation 411 is 0, the LAA cell may perform channeloccupancy and data transmission in operation 405.

Meanwhile, unless the variable N is 0 in operation 411, the LAA cell mayperform the second channel sensing operation again in operation 408.When the channel sensed in operation 408 is determined not to be an idlechannel in operation 409, the LAA cell may perform a third channelsensing operation in operation 412. The third channel sensing operationmay be set to be the same as the first channel sensing operation or thesecond channel sensing operation. Further, the third channel sensingoperation may be set to perform the operation of creating a time delaywithout a separate channel sensing or channel occupancy operation.

The third channel sensing time during which the third channel sensingoperation may be performed may be set to be the same or different fromat least one of the first channel sensing time or the second channelsensing time. When the third channel sensing operation is set to be thesame as the first channel sensing operation or the second channelsensing operation, the LAA cell determines a result of the channelsensing in operation 413. When the channel sensed by the third channelsensing operation is in the idle state in operation 413, the LAA cellmay perform the second channel sensing operation again in operation 408.When determining that the sensed channel is not in the idle state inoperation 413, the LAA cell performs the third channel sensing operationin operation 412.

As set forth above, a contention window may be reconfigured. Here, thecontention window may be set using, e.g., the number of times ofattempting to occupy the channel, occupancy rate for the channel (e.g.,traffic load), or result of receiving data signals transmitted uponchannel occupancy by the UE (e.g., A/N). However, when the contentionwindow may be reset using the result of receiving the transmission datasignal by the UE, for the LAA that may receive A/N from one or more UEsat the same time, the reference for resetting the contention window maybe unclear. Accordingly, according to the present disclosure, there isproposed a method for resetting the contention window using the resultof receiving the data transmitted from the base station by the UE.

FIG. 5 is a view illustrating the temporal relation between LAA cell andUEs according to data communication according to an embodiment of thepresent disclosure.

FIG. 5 illustrates an example in which the LAA cell 505 performs datacommunication with the UE1 510 and the UE2 511.

Referring to FIG. 5, the LAA cell 505 performs a channel sensingoperation during the channel sensing interval 520 to occupy a channeldetermined to be in the idle state. The LAA cell 505 may perform thechannel sensing operation according to the scheme described above inconnection with FIG. 4. The LAA cell 505 may use the occupied channelduring the channel occupancy interval 530. The LAA cell 505 may transmita signal 525 for indicating the channel occupancy according to the timewhen the channel occupancy starts until before the start time 515 of thesubframe. The signal for indicating the channel occupancy may include atleast one of a PSS/SSS/CRS and a newly defined signal.

The LAA cell 505 may transmit data to the UE1 510 and the UE2 511through data scheduling during the channel occupancy interval 530. TheUE1 510 receives data in subframes n, n+1, n+3, and n+4 of the channeloccupancy interval 530. The UE2 511 receives data in subframes n, n+2,n+3, and n+4.

The LAA cell 505 may transmit data using different frequency resources(e.g., resource blocks) for the UE1 510 and the UE2 511 in subframe n515. For the FDD system, the UE1 510 and the UE2 511 receiving data insubframe n 515, respectively, transmit data reception results 550 and555 to the LAA cell 505 in subframe n+4. The LAA cell 505 may performdata retransmission depending on the data reception results.

In other words, the LAA cell may transmit data to the UE1 510 and theUE2 511 during the channel occupancy interval 530 and may then receivethe data reception results from the UE1 510 and the UE2 511 during theperiod from subframe n+4 to subframe n+8. Here, the LAA cell 505 mayreset the contention window for channel sensing operation using thereceived data reception results.

References for the LAA cell 505 to reset the contention window may beset as follows.

Method 1. Reset contention window based on the reception result of UEfor all the data transmitted during channel occupancy interval.

Method 2. Reset contention window based on the reception result of UEfor data transmitted in the last time (or the last full subframe) of thechannel occupancy interval.

Method 3. Reset contention window based on the reception result of UEfor data transmitted before a preset time of the channel occupancyinterval.

Method 4. Reset contention window based on the reception result of UEfor data transmitted after a preset time of the channel occupancyinterval.

Operations according to the above methods are described below. The LAAcell 505 (or base station) may transmit data to the UE1 510 and the UE2511 during the channel occupancy interval 530 and may receive as per adefined time the result (A/N) of data reception by the UE for the datatransmitted as per A/N transmission time relation between base stationand UE newly defined for operation of the LAA cell 505 or duplex scheme(e.g., FDD or time division duplexing (TDD)) set for the cell. Here, theLAA cell 505 may reset the contention window for a next channel sensingoperation using all or some of the data reception results received fromthe UE1 510 and the UE2 511.

This is described below in more detail with reference to FIG. 5.Although an example is assumed and described where the LAA cell 505operates based on an FDD scheme for ease of description, it may also beapplicable to the cases where the LAA cell 505 operates based on a TDDscheme or a separately defined scheme.

When the LAA cell 505 operates based on the FDD scheme, the UE1 510 andthe UE2 511 receiving data from the LAA cell 505 in subframe n transmitthe reception results 550 and 555, respectively, of the data to the LAAcell 505 in subframe n+4. Accordingly, the LAA cell 505 may receive thedata reception results from the UE1 510 and the UE2 511 according to thechannel occupancy interval 530 in the interval [n+4 to n+8]. Here, theinterval during which A/Ns are received from the UEs to reset thecontention window (hereinafter, referred to as a contention windowconfiguration reference time) may be set as follows.

Method A-1. Time during which the LAA cell receives data receptionresults from all or some UEs for all the data transmitted during thechannel occupancy interval of the LAA cell.

Method A-2. Time during which the LAA cell receives data receptionresults from all or some UEs for the data transmitted at the last datatransmission time within the channel occupancy interval of the LAA cell.

Method A-3. Time during which the LAA cell receives data receptionresults from all or some UEs for the data transmitted at the first datatransmission time within the channel occupancy interval of the LAA cell.

Method A-4. Time during which the LAA cell receives data receptionresults from all or some UEs for the data transmitted at a particulartime within the channel occupancy interval of the LAA cell.

Method A-5. Time during which the LAA cell receives data receptionresults from all or some UEs for the data transmitted before or after aparticular time within the channel occupancy interval of the LAA cell.

Method A-6. Time previously set or defined.

Method A-1 is described with reference to FIG. 5. The LAA cell 505receives data reception results 550, 560, 570, 580, 555, 565, 575, and585 from the UE1 510 and the UE2 511 in the interval [n+4 to n+8] forthe data transmitted during the channel occupancy interval 530. Theinterval [n+4 to n+8] may be set as the contention window configurationreference time for resetting the contention window. That is, the LAAcell 505 may set the interval for receiving the data reception resultsof the UE for the data transmitted during a particular channel occupancyinterval as the contention window configuration reference time forresetting the contention window.

Method A-2 is described with reference to FIG. 5. The LAA cell 505receives data reception results 550, 560, 570, 580, 555, 565, 575, and585 from the UE1 510 and the UE2 511 in the interval [n+4 to n+8] forthe data transmitted during the channel occupancy interval 530. Here,the LAA cell 505 may set the interval n+8 for receiving the datareception results 550 and 555 of the UEs 510 and 511 for the datatransmitted in the last subframe n+4 having the last data transmissiontime (or lms subframe 515) requiring A/N transmission of the channeloccupancy interval 530 as the contention window configuration referencetime for resetting the contention window.

Method A-3 is described with reference to FIG. 5. The LAA cell 505receives data reception results 550, 560, 570, 580, 555, 565, 575, and585 from the UE1 510 and the UE2 511 in the interval [n+4 to n+8] forthe data transmitted during the channel occupancy interval 530. Here,the LAA cell 505 may set the interval n+4 for receiving the datareception results of the UE for data transmitted in the first subframe nhaving the first data transmission time (or 1 ms subframe) requiring theA/N transmission of the channel occupancy interval 530 as the contentionwindow configuration reference time for resetting the contention window.

Methods A-3 and A-5 are described with reference to FIG. 5. The LAA cell505 receives data reception results 550, 560, 570, 580, 555, 565, 575,and 585 from the UE1 510 and the UE2 511 in the interval [n+4 to n+8]for the data transmitted during the channel occupancy interval 530.Here, the LAA cell 505 may set the interval for receiving the datareception results of the UE for data transmitted in a particularsubframe or before or after the particular subframe in the datatransmission time (or lms subframe) requiring the A/N transmission ofthe channel occupancy interval 530 as the contention windowconfiguration reference time for resetting the contention window.

For example, the contention window configuration reference time may beset according to a previously defined A/N transmission time relation ofUE between the LAA cell 505 and the UE. When the FDD scheme is used, thepreviously defined A/N transmission time relation of UE between the LAAcell 505 and the UE indicates that an A/N needs to be transmitted 4 msafter the time when the LAA cell 505 transmits data. Accordingly, theLAA cell 505 may set the contention window configuration reference timeusing the A/N transmission time relation of UE with respect to thechannel occupancy interval 530.

For example, a subframe before the A/N transmission time relation of UEpre-defined with respect to the latest data transmission time (or last 1ms subframe) of the channel occupancy interval 530 may be set as thecontention window configuration reference time. That is, the A/Ntransmission interval n+4 for subframe n, e.g., the subframe before theA/N transmission time relation for n+4 which is the last channeloccupancy time of the channel occupancy interval 530, may be set as thecontention window configuration reference time. Here, as in method A-5,the interval before or after subframe n+4 including subframe n may beset as the contention window configuration reference time.

Method A-6 is described with reference to FIG. 5. Time A set by the LAAcell or previously set with respect to the time n when the LAA cell 505starts to transmit data in the channel occupancy interval 530 or thetime n+4 when the LAA cell starts to receive data reception results fromthe UE1 510 and the UE2 511 for data transmitted during the channeloccupancy interval 530 may be set as the contention window configurationreference time. For example, when A=100 ms, the LAA cell 500 may set aninterval that is within 100 ms (n+100 or n+104) of the time n when theLAA cell starts to transmit data or the start time n+4 when the LAA cellstarts to receive data reception results from the UE1 510 and the UE2511 for transmitted data may be set as the contention windowconfiguration reference time.

Here, the LAA cell 505 may use the A/N information received from some orall UEs during the set contention window configuration reference timefor resetting the contention window. For example, all the UEstransmitting results of data reception during the contention windowconfiguration reference time may be set as contention window varyingreference UEs. As another example, the LAA cell 505 may select some UEsfrom all of the UEs transmitting the data reception results in thecontention window configuration reference time based on channel qualityinformation (or an allocated modulation and coding scheme (MCS) value)and set them as the contention window varying reference UEs.

For example, the LAA cell 505 may set the UE having received anallocation of the lowest MCS value within the contention windowconfiguration reference time or the UE having received an allocation ofan MCS value within the range selected by the LAA cell 505 or previouslyset as the contention window varying reference UEs. In other words, theUE having the lowest MCS may be considered the UE receiving largestinterference from adjacent devices, and the UE may be used as acontention window varying reference UE. Or, among the UEs transmittingdata reception results during the contention window configurationreference time, the LAA cell 505 may set the UE having latesttransferred measured channel information to the LAA cell 505 or the UEhaving transferred a signal separately defined to transfer the UEchannel environment as the contention window varying reference UE.

The LAA cell 505 may set a reference UE for resetting the contentionwindow by the above methods alone or in combination. Further, thecontention window configuration reference time may be set by the abovemethods not alone, but by combinations or expanding the methods as well.As an example, in method 1, the contention window configurationreference time may be set with respect to one or more channel sensingintervals of the LAA cell. For example, the interval corresponding totwo channel occupancy intervals 530 and 535 may be set as the contentionwindow configuration reference time. The methods and examples suggestedabove are merely examples and the present disclosure is not limitedthereto.

The LAA cell 505 may reset the contention window for the next channelsensing operation using all or some of the data reception resultsreceived from the UE using the above methods alone or combinations ofthe above methods. Here, the LAA cell 505 may use the following methodsto vary the contention window applied to the next channel sensingoperation using the A/N information received from the contention windowconfiguration reference UE and the contention window configurationreference time.

Method B-1. When at least one or more NACKs are received from thecontention window configuration reference UE during the contentionwindow configuration reference time, increase the contention windowapplied to the next channel sensing operation.

Method B-2. Increase or reduce the contention window applied to the nextchannel sensing operation based on the ratio or number of NACKs (orACKs) received from the contention window configuration reference UEduring the contention window configuration reference time.

Method B-1 is described in greater detail with reference to FIG. 5. Whenthe contention window configuration reference time is set to [n+4 ton+8] corresponding to the channel occupancy interval 530 of the LAA cell505 as by method A-1, and all the UEs transmitting the data receptionresults during the contention window configuration reference time areset as the contention window configuration reference UEs, the LAA cell505 may increase the contention window since the LAA cell 505 hasreceived the NACK 555 from UE2 511 during the contention windowconfiguration reference time set as above. Here, an example ofincreasing the contention window may be to use a scheme of exponentiallyincreasing the contention window (e.g., 16→32→64→128, →1024). Theexponentially increasing scheme is an example, and the contention windowmay be varied by other methods including, e.g., a linearly increasingscheme or sequentially or arbitrarily selecting one of contention windowcandidate values (or set, {16, 32, 64, 256, 1024}).

When the LAA cell 505 fails to receive ACKs or NACKs from the contentionwindow configuration reference UEs during the contention windowconfiguration reference time as set, the LAA cell 505 may determine tohave received an NACK to increase the contention window or reuse thepreset contention window. When the LAA cell 505 does not receive NACKsfrom the contention window configuration reference UEs during thecontention window configuration reference time as set, the LAA cell 505does not vary the contention window or may vary the contention window tothe initial set value.

Method B-2 is described in greater detail with reference to FIG. 5. Whenthe contention window configuration reference time of the LAA cell 505is set to [n+4 to n+8] corresponding to the channel occupancy interval530 of the LAA cell 505, and all the UEs transmitting the data receptionresults during the contention window configuration reference time areset as the contention window configuration reference UEs, the LAA cell505 may one NACK 555 from the UE2 511 during the set contention windowconfiguration reference time as shown in FIG. 5. In such scenario, whenthe case where two or more NACKs or P % (e.g., 10%) or more NACKs arereceived is set to the contention window variation reference based onmethod B-2, the LAA cell 505 does not vary the contention window or mayreset the contention window to the initial contention window.

When the LAA cell 505 receives two or more NACKs or P % or more NACKsfrom the contention window configuration reference UEs during the setcontention window configuration reference time, the LAA cell 505 mayvary the contention window. An example of varying the contention windowmay be to use a scheme of exponentially increasing the contention window(e.g., 16→32→64→128→ . . . →1024) or a scheme of exponentiallydecreasing the contention window (e.g., 1024→512→ . . . 432→16). Theexponentially increasing scheme is an example and may include e.g., alinearly increasing scheme or sequentially or arbitrarily selecting oneof contention window candidate values (or set, {16, 32, 64, 256, 1024}).

When the LAA cell 505 fails to receive ACKs or NACKs from the contentionwindow configuration reference UEs during the contention windowconfiguration reference time as set, the LAA cell 505 may determine tohave received an NACK to increase the contention window or reuse thepreset contention window.

FIG. 6 is a view illustrating an example in which a contention window isconfigured per transmission of data and control information according toan embodiment of the present disclosure.

Referring to FIG. 6, the LAA cell 600 may differently set the way ofincreasing or decreasing the contention window depending on the type ofsignal to be transferred by occupying the channel of the LAA cell 600.For example, for channel occupancy for normal data transmission(PDSCH/physical uplink shared channel (PUSCH)), a contention windowincreasing scheme using exponentially increasing scheme applies, and forchannel occupancy for transferring control information((E)PDCCH/discovery RS, SRS, or CSI-RS), the contention window is set tothe initial period to be recycled or a linearly increasing scheme may beutilized.

The contention window varied by the reference and scheme may be appliedto the channel sensing operation (e.g., the second channel sensingoperation) that occurs after the time that the contention windowconfiguration reference time and contention window configurationreference UE, contention window variation reference and method aredetermined. However, since a channel sensing operation may be performedbefore varying the contention window as described above, there is a needfor a contention window configuration for the channel sensing operationperformed before the contention window varying time. This is describedbelow in detail with reference to FIG. 6.

The LAA cell 600 performs the channel sensing operation during a presetcontention window 610 in order to transmit data to the UE 605. The LAAcell 600 determines a channel that is in an idle state depending on thechannel sensing operation. The LAA cell 600 may occupy and use thechannel during the channel occupancy interval 620. Accordingly, the LAAcell 600 transmits data to the UE 605 during the channel occupancyinterval 620.

Here, it is assumed that the contention window configuration referencetime of the LAA cell 600 has been set based on method A-2, all the UEstransmitting data reception results during the contention windowconfiguration reference time have been set to contention windowconfiguration reference UEs, and the method for varying the contentionwindow has been set based on method B-1. Then, the LAA cell 600 variesthe contention window based on the A/N 674 for the last subframe amongthe A/Ns for data transmitted during the channel occupancy interval 620.

However, as shown in FIG. 6, the LAA cell 600 may re-perform the channelsensing operation 630 for additional channel occupancy before receivingthe A/N 670 for the channel sensing interval 630, i.e., before the timeof varying the contention window, and may then occupy the channeloccupancy interval 640 depending on the channel sensing result. In thegeneral Wi-Fi system, when the channel is occupied and then re-occupied,the contention window is varied. That is, the contention window isincreased or decreased depending on the data reception result of the UEduring the channel occupancy interval. For the LAA cell 600, however,since a channel sensing operation 630 may be performed before varyingthe contention window as described above, there is a need forconfiguring the contention window for the channel sensing operation 630performed before the contention window varying time.

The contention window for the channel sensing operation 630 performedbefore varying the contention window may be set by the followingmethods.

Method C-1. Reuse the contention window set upon previous channeloccupancy.

Method C-2. Use initial contention window value.

Method C-3. Vary depending on UE reception capability received beforechannel sensing operation.

Method C-1 is described below in greater detail. The contention windowfor the channel sensing operation 630 performed before the time ofvarying the contention window as shown in FIG. 6 may be set to beidentical to the contention window used for the latest channel sensingoperation in preset contention window 610. Another method is to performthe channel sensing operation 630 using the initial contention windowvalue as the contention window for the channel sensing operation 630performed before the time of varying the contention window or topreviously define and use, as a particular interval, the contentionwindow for the channel sensing operation 630 performed before the timeof varying the contention window as described above. Still anothermethod is to vary using the A/N information of the UE received beforethe channel sensing operation 630 performed before the time of varyingthe contention window. Here, the contention window may be varied usingthe A/N information of the UE as received by excluding or varying toanother scheme at least one reference among the contention windowconfiguration reference UE and the contention window configurationreference time as set above.

The LAA cell 600 may occupy the channel through the channel sensingoperation 650 when attempting to re-occupy the channel after the channeloccupancy interval 640. Here, the channel sensing operation 650 may beperformed using the contention window previously varied.

Further, the LAA cell 600 may use other contention window without usingthe already varied contention window on the channel sensing operationperformed before the contention window varying time. In other words, thechannel sensing operation may be performed by abstaining from using thealready varied contention window or applying a separately definedcontention window depending on the type of signal to be transferred bythe LAA cell 600 occupying the channel.

For example, for the channel occupancy for normal data transmission(PDSCH/PUSCH) (e.g., 620, 640, and 660), a previously changed contentionwindow may be used to perform channel sensing operation. Here, whenchannel occupancy is attempted to transfer control information (e.g.,(E)PDCCH, discovery RS, SRS, CSI-RS, etc.) 685, the already variedcontention window and other contention window 680 may be used. Forexample, it may be varied to the initially set contention window andused, or a contention window separately set for transfer of controlinformation may be used to perform channel sensing operation. Here, thechannel may be occupied and used without performing a separate channelsensing operation to transfer the control information. When the channelis reoccupied for general data transmission 695 after occupying thechannel for control information transfer, the LAA cell 600 may perform achannel sensing operation by using or setting the already set contentionwindow (e.g., the contention window varied through the channel occupancyinterval 660) or the contention window (contention window in 650) usedupon channel occupancy for existing data transmission to the initialcontention window.

FIG. 7 is a flowchart illustrating a method for configuring a contentionwindow for a channel sensing operation according to an embodiment of thepresent disclosure.

Referring to FIG. 7, the LAA cell sets a contention window configurationreference time in operation 701. The LAA cell may set the contentionwindow configuration reference time to a particular time set using thewhole or part of the A/N transmission interval of the UE for the channeloccupancy time or A/N transmission time relation.

The LAA cell sets a contention window configuration reference UE inoperation 702. The LAA cell may set all or some of the UEs performingA/N transmission in the contention window configuration reference timeas contention window configuration reference UEs.

The LAA cell sets a contention window varying reference in operation703. That is, the LAA cell sets the contention window reference basedon, e.g., the number or ratio of A/Ns received as per operations 701 and702.

The LAA cell receives a data reception result transmitted from thecontention window configuration reference UE in operation 704. The LAAcell determines whether to vary the contention window in operation 705based on the contention window varying reference set in operations 701,702, and 703. For example, the LAA cell receives response signals formultiple data transmitted in the first (or start) subframe of continuoussubframes transmitted latest by the LAA cell where response signals maybe fed back. The first subframe indicates a subframe where A/N feedbackis available in the base station. The LAA cell may determine whether tovary or maintain the contention window based on whether a ratio of NACKsignals to the response signals is a preset ratio or more.

When the contention window needs to be increased (e.g., when the ratioof NACKs to the response signals is a predetermined ration (e.g., 80%)or more), the LAA cell increases the contention window by the contentionwindow increasing scheme set in operation 706.

When the contention window need not be increased (e.g., when the ratioof NACKs to the response signals is less than the predetermined ratio),the LAA cell reduces the contention window by the contention windowdecreasing scheme set in operation 707, maintain the existing contentionwindow, or set the contention window to the initial value.

FIG. 8 is a block diagram illustrating a base station according to anembodiment of the present disclosure.

Referring to FIG. 8, the base station includes a controller 800, atransmitter 810, and a receiver 820. The controller 800, the transmitter810, and the receiver 820 perform the above-described channel occupancyoperation and contention window configuration operation on theunlicensed band.

The receiver 820 receives signals from the base station or UE orperforms an operation for measuring a channel from the base station orUE. The receiver 820 may perform an operation for sensing the unlicensedband channel using a value set for the channel sensing operation setthrough the controller 800.

The controller 800 may determine whether the unlicensed band is in anidle state based on information on the unlicensed band sensed by thereceiver 820. When it is determined that the unlicensed band is in theidle state, the controller 800 may control the transmitter 810 totransmit a signal for channel occupancy or control channel and datachannel information for a particular UE. When it is determined that theunlicensed band is not in the idle state, the controller 800 may controlthe receiver 820 to continue to perform the channel sensing operation.

The controller 800 may set control channel transmission parameters suchas PDCCH/EPDCCH for a particular UE, reference signal transmissionparameters of various types, and determine all or some of variables usedin a channel sensing operation and parameters required to be set ortransferred between the base station and the UE including PDSCH/EPDSCHscheduling. The parameters between the base station and the UE set bythe controller 800 may be sent to the UE by controlling the transmitter810.

FIG. 9 is a block diagram illustrating a UE according to an embodimentof the present disclosure.

Referring to FIG. 9, the UE includes a controller 900, a transmitter910, and a receiver 920.

The controller 900 controls the receiver 920 to receive configurationinformation between base station and UE for signal transmission on thelicensed band and unlicensed band from the base station and uses theunlicensed band based on the received configuration information. Thecontroller 900 may obtain the state information of the unlicensed bandusing at least one of a set value for determining whether scheduling maybe made in the subframe where the channel sensing operation is performedas set by the base station and received via the receiver 920, a setvalue for the signal transmitted through the channel occupancy startsymbol of the base station, and unlicensed band state information thatmay be transmitted to the UE by the base station using the licensed bandor other unlicensed band. Further, the controller 900 may determine theresult of reception of the data signal received from the base stationand may control the transmitter 910 to notify the base station of thedata reception result.

The controller 900 may determine the PDSCH/EPDSCH scheduling informationfrom the control information received by the receiver 920. Further, thecontroller 900 may include a decoder that receives the PDSCH/EPDSCHthrough the receiver 920 and decodes the PDSCH/EPDSCH.

As is apparent from the foregoing description, according to anembodiment of the present disclosure, it may be possible to reduce thenumber of times of blind detection by the receiver that determineswhether channel is occupied in order to determine whether thetransmitter, among devices using unlicensed band, occupies channel.

According to an embodiment of the present disclosure, a contentionwindow in an unlicensed band may be effectively adjusted and used in awireless communication system, allowing the unlicensed band channel tobe effectively used as an additional channel for communication.

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for managing a contention window by abase station in a wireless communication system, the method comprising:transmitting multiple data in a first subframe; obtaining values ofreception result corresponding to the multiple data; determining a ratioof negative acknowledge (NACK) signals to the values of receptionresult; adjusting or maintaining the contention window based on thedetermined ratio; setting a value within the contention window as acounter value; sensing the channel during a first interval to determinewhether the sensed channel is idle; if the channel is idle, reducing thecounter value and transmitting data in a second subframe using thechannel based on the counter value; and if the channel is not idle,sensing the channel during a second interval.